The compound 7-[(3R)-3-aminohexahydro-1H-azepin-1-yl]-8-chloro-1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxoquinoline-3-carboxylic acid and its hydrochloride salt generally known by name, Besifloxacin hydrochloride of Formula-II is an antibacterial agent and have activity against Gram-negative and Gram-positive bacteria.

Besifloxacin hydrochloride of Formula-II is disclosed in U.S. Pat. No. 5,447,926 (U.S. Pat. No. '926). Preparative process described in this patent is carried out by: (a) reacting 1-cyclopropyl-6,7-difluoro-4-oxo-1,4-dihydroquinoline-3-carboxylic acid of Formula-III with (R)-azepan-3-amine of Formula-IV in acetonitrile followed by chlorination in presence of sulfuryl chloride to give Besifloxacin of Formula-VI, which is purified through column chromatography. The reaction sequence is shown in scheme-1.

The major drawback of the above said process is poor yield and purity of Besifloxacin. The reaction method disclosed in U.S. Pat. No. '926; requires large time for completion, hence not suitable for plant scale production. Also use of column chromatography for purification purpose is neither economical nor environmental friendly, especially when performed at large scale.
PCT application no. WO2008/045673, describes process for preparation of Besifloxacin of Formula-VI which encompasses use of intermediate, 8-chloro-1-cyclopropyl-6-fluoro-7-(3-((3-nitrobenzylidene)amino)azepan-1-yl)-4-oxo-1,4-dihydroquinoline-3-carboxylic acid of Formula-IX as shown in Scheme-2.

The major drawback of the above said process is use of side chain of Formula-VIII, which requires coupling of 3-amino azepane with nitro benzaldehyde. Nitro benzaldehyde is an expensive reagent and making of same is not a good option especially at large scale, as nitration in itself is a hazardous process and is unfriendly for human and environment.
US Patent application no. 2008/0176834, describes use of intermediate of Formula-X in preparation of Besifloxacin as shown in Scheme-3.

There are two major drawbacks in above said process such as use of a) expensive reagent of Formula-VIII and b) large volume of sulfuryl chloride, thereby making process highly uneconomical.
Therefore, there is a need to develop a new process for preparation of Besifloxacin hydrochloride in high yield that encompasses use of economic and environmental friendly reagents and intermediates.
The present inventors have worked on the development of new process for preparation of Besifloxacin hydrochloride through novel fluoroquinolone carboxylic acid intermediates prepared by the use of inexpensive, easily available, human as well as environmental friendly reagents.